EPIDEMIOLOGY QUESTIONS
What are the different types of epidemiological studies? Give advantages and disadvantages of each. Epidemiological studies fall into two broad groups. These are experimental studies, where the epidemiologists have control over their experiment/circumstances or observational studies where they do not. Clinical trials are a good example of the experimental process; here specific drugs/treatments are used and their effects on a sample group analyzed. Observational studies are further divided into descriptive and analytical studies. In a descriptive study, information is collected to summarize a health event or problem. We may ask who, when and where questions to determine what happened. In analytical studies, comparisons are made between groups to determine the role of various risk factors in causing the problem. Analytical studies focus on the how and why questions in health events or problems. The two main types of observational studies are the cohort study and the case control study. Cohort studies are similar to experimental studies in that we categorize subjects on the basis of their exposure and then observe to determine if they develop the health conditions we are studying. What makes cohort studies different from experimental studies is that here; you study the population according to their exposure rather than determine it by trial. Cohort studies are referred to as prospective studies since they follow the study populations forward in time, from suspected cause to effect e.g. following a group of people on the basis of their smoking status so see if they develop lung cancer over time. Cohort studies have several advantages: *You can examine multiple outcomes for a single exposure. For instance, if you select a group based on their smoking exposure, you can look not only at the incidence of lung cancer, but also at the incidence of cardiovascular disease, emphysema, burns, other smoking-related outcomes. *Cohort studies are very useful in examining rare exposures, such as asbestos exposure and lung cancer. *You can directly calculate the incidence of disease for each of the exposure groups. *The temporal sequence is logical: you are starting with exposure and following forward in time to the development of disease. Disadvantages of cohort studies are: *They are costly in time and resources. *If the disease is rare, you need a large number of subjects. *Because you are following forward in time, logistical problems may *develop and subjects can be lost to follow-up. The other type of observational study is called the case-control study. Here the epidemiologist is working backward in time from the effect back to the suspected cause. This is why case-control studies are referred to as retrospective studies. Participants are selected on the basis of whether they have the disease or not and separated into two groups on this basis. The group with the health problem is called the case subjects, the group without is called the controls. These groups are then compared to determine the presence of specific exposures or risk factors. E.g. you could pick a group of people with lung cancer and a group without; then compare them for their history of exposure to smoking. The relationship between exposure and outcome in a case-control study is then quantified by calculations. Case-control studies have three primary advantages: *You can examine multiple exposures for a single outcome. *They are well suited for studying rare diseases and those with long latency periods. *They require fewer case-subjects and are generally quicker and less expensive to conduct than cohort studies, which makes them well suited for the conditions of an outbreak investigation. The disadvantages of case-control studies are: *They aren't suitable for studying rare exposures. *They are subject to bias because of the method used to select controls; and they don't allow you to directly measure the incidence of disease. *Because they look backward, case-control studies may create uncertainty about the relationship in time between exposure and disease. What is the epidemiological triangle? ''' '''It is the interplay between three factors: